The invention relates to the field of televisions, for example those televisions having a wide display format ratio screen, which must interpolate video data to implement various display formats. Most televisions today have a format display ratio, horizontal width to vertical height, of 4:3. A wide format display ratio corresponds more closely to the display format ratio of movies, for example 16:9. The invention is applicable to both direct view televisions and projection televisions.
Televisions having a format display ratio of 4:3, often referred to as 4.times.3, are limited in the ways that single and multiple video signal sources can be displayed. Television signal transmissions of commercial broadcasters, except for experimental material, are broadcast with a 4.times.3 format display ratio. Many viewers find the 4.times.3 display format less pleasing than the wider format display ratio associated with the movies. Televisions with a wide format display ratio provide not only a more pleasing display, but are capable of displaying wide display format signal sources in a corresponding wide display format. Movies "look" like movies, not cropped or distorted versions thereof. The video source need not be cropped, either when converted from film to video, for example with a telecine device, or by processors in the television.
Televisions with a wide display format ratio are also suited to a wide variety of displays for both conventional and wide display format signals, as well as combinations thereof in multiple picture displays. However, the use of a wide display ratio screen entails numerous problems. Changing the display format ratios of multiple signal sources, developing consistent timing signals from asynchronous but simultaneously displayed sources, switching between multiple sources to generate multiple picture displays, and providing high resolution pictures from compressed data signals are general categories of such problems. Such problems are solved in a wide screen television according to this invention. A wide screen television according to various inventive arrangements is capable of providing high resolution, single and multiple picture displays, from single and multiple sources having similar or different format ratios, and with selectable display format ratios.
Televisions with a wide display format ratio can be implemented in television systems displaying video signals both at basic or standard horizontal scanning rates and multiples thereof, as well as by both interlaced and noninterlaced scanning. Standard NTSC video signals, for example, are displayed by interlacing the successive fields of each video frame, each field being generated by a raster scanning operation at a basic or standard horizontal scanning rate of approximately 15,734 Hz. The basic scanning rate for video signals is variously referred to as f.sub.H, 1f.sub.H, and 1H. The actual frequency of a 1f.sub.H signal will vary according to different video standards. In accordance with efforts to improve the picture quality of television apparatus, systems have been developed for is displaying video signals progressively, in a noninterlaced fashion. Progressive scanning requires that each displayed frame must be scanned in the same time period allotted for scanning one of the two fields of the interlaced format. Flicker free AA-BB displays require that each field be scanned twice, consecutively. In each case, the horizontal scanning frequency must be twice that of the standard horizontal frequency. The scanning rate for such progressively scanned or flicker free displays is variously referred to as 2f.sub.H and 2H. A 2f.sub.H scanning frequency according to standards in the United States, for example, is approximately 31,468 Hz.
Considerable signal processing of the main video signal is necessary to implement many of the display formats which are especially appropriate for a wide screen television. The video data must be selectively compressed and expanded, depending upon the desired format. In one case, for example, it is necessary to compress the 4.times.3 NTSC video by a factor of 4/3, or 4:3, to avoid aspect ratio distortion of the displayed picture. In the other case, for example, the video can be expanded to perform horizontal zooming operations usually accompanied by vertical zooming. Horizontal zoom operations up to 33% can be accomplished by performing compressions less than 4/3, for example 5/4. A sample interpolator is used to recalculate the incoming video to a new pixel, positions because the luminance video bandwidth, up to 5.5 MHz for S-VHS format, occupies a large percentage of the Nyquist or fold over frequency, which is 8 MHz for a 1024f.sub.H system clock.